Herd immunity, a process in which resistant individuals limit the spread of a pathogen among susceptible hosts has been extensively studied in eukaryotes. Even though bacteria have evolved multiple immune systems against their phage pathogens, herd immunity in bacteria remains unexplored. Here we experimentally demonstrate that herd immunity arises during phage epidemics in structured and unstructured Escherichia coli populations consisting of differing frequencies of susceptible and resistant cells harboring CRISPR immunity. In addition, we develop a mathematical model that quantifies how herd immunity is affected by spatial population structure, bacterial growth rate, and phage replication rate. Using our model we infer a general epidemiological rule describing the relative speed of an epidemic in partially resistant spatially structured populations. Our experimental and theoretical findings indicate that herd immunity may be important in bacterial communities, allowing for stable coexistence of bacteria and their phages and the maintenance of polymorphism in bacterial immunity.
10%susceptible
Time-lapse images of spread of T7 phage epidemics in Escherichia coli spatially structured populations over 48 hours. Archive contains images of the following treatment: 10% susceptible, 90% resistant cells.
20%susceptible
Time-lapse images of spread of T7 phage epidemics in Escherichia coli spatially structured populations over 48 hours. Archive contains images of the following treatment: 20% susceptible, 80% resistant cells.
30%susceptible
Time-lapse images of spread of T7 phage epidemics in Escherichia coli spatially structured populations over 48 hours. Archive contains images of the following treatment: 30% susceptible, 70% resistant cells.
40%susceptible
Time-lapse images of spread of T7 phage epidemics in Escherichia coli spatially structured populations over 48 hours. Archive contains images of the following treatment: 40% susceptible, 60% resistant cells.
50%susceptible
Time-lapse images of spread of T7 phage epidemics in Escherichia coli spatially structured populations over 48 hours. Archive contains images of the following treatment: 50% susceptible, 50% resistant cells.
60%susceptible
Time-lapse images of spread of T7 phage epidemics in Escherichia coli spatially structured populations over 48 hours. Archive contains images of the following treatment: 60% susceptible, 40% resistant cells.
70%susceptible
Time-lapse images of spread of T7 phage epidemics in Escherichia coli spatially structured populations over 48 hours. Archive contains images of the following treatment: 70% susceptible, 30% resistant cells.
80%susceptible
Time-lapse images of spread of T7 phage epidemics in Escherichia coli spatially structured populations over 48 hours. Archive contains images of the following treatment: 80% susceptible, 20% resistant cells.
90%susceptible
Time-lapse images of spread of T7 phage epidemics in Escherichia coli spatially structured populations over 48 hours. Archive contains images of the following treatment: 90% susceptible, 10% resistant cells.
100%susceptible_control_run1
Time-lapse images of spread of T7 phage epidemics in Escherichia coli spatially structured populations over 48 hours. Archive contains images of the following treatment: all 100% susceptible controls of run 1.
100%susceptible_control_run2
Time-lapse images of spread of T7 phage epidemics in Escherichia coli spatially structured populations over 48 hours. Archive contains images of the following treatment: all 100% susceptible controls of run 2.
100%susceptible_control_run3
Time-lapse images of spread of T7 phage epidemics in Escherichia coli spatially structured populations over 48 hours. Archive contains images of the following treatment: all 100% susceptible controls of run 3.
